Uninterruptible power supply (UPS) equipment, as a type of emergency power supply, is suitable for providing high-quality voltage, frequency and waveform AC power without time interruption to users' critical equipment (such as bank clearing centers, data centers, securities trading and futures trading systems, etc.).

It is composed of power converters (rectifiers, inverters), transfer switches (electronic or mechanical), energy storage devices (such as batteries), and control systems, etc. It is a power supply equipment that maintains the continuity of the load power when the input power supply fails. The online UPS is usually adopted.

Its working principle is to first convert the alternating current power input from the mains into a stabilized direct current power supply, which is then supplied to the battery and inverter. After that, it is re-transformed into a stable, pure and high-quality alternating current power supply through the inverter. It can completely eliminate any power supply problems that may occur in the input power supply (voltage fluctuation, frequency fluctuation, harmonic distortion and various interferences). When the input of the mains power is normal, the UPS stabilizes the mains power and supplies it to the load for use. At this time, the UPS is an AC mains power stabilizer, and it also charges the battery inside the machine. When the mains power is interrupted (due to an accident), the UPS immediately supplies 220V AC power to the load by converting the battery energy inside the machine through an inverter.

When choosing an uninterruptible power supply (UPS) device, factors such as the nature of the load, load capacity, and the allowable interruption time of power supply should be taken into account. The UPS should be able to operate normally at an altitude of 1000m or less under rated conditions. When the altitude exceeds 1,000 meters, the capacity should be reduced for use. For example, a UPS with a rated capacity of 1000 KVA should be loaded at an altitude of 1000 meters or less with a capacity of 1000 KVA. When the altitude reaches 1,500 meters, the load should be carried at a capacity of 950 KVA. When the altitude exceeds 5,000 meters, a 670 KVA UPS should be used to carry the load.